Synthesis, characterization, and catalytic properties of new half-sandwich zirconium(iv) complexes

Abstract

A number of new half-sandwich zirconium(IV) complexes bearing N,N-dimethylaniline-amido ligands with the general formula Cp*ZrCl₂[ortho-(RNCH₂)(Me₂N)C₆H₄] [R = 2,6-Me₂C₆H₃ (1), 2,6-ⁱPr₂C₆H₃ (2), ⁱPr (3), ^tBu (4)] were synthesized by the reaction of Cp*ZrCl₃ with the corresponding ortho-(Me₂N)C₆H₄CH₂NRLi. All new zirconium complexes were characterized by ¹H and ¹³C NMR, elemental analyses and single crystal X-ray diffraction analysis. The molecular structural analysis reveals that the NMe₂ group does not coordinate to the zirconium atom in all cases. Complexes 1–4 all have a pseudo-tetrahedral coordination environment in their solid state structures and adopt a three-legged piano stool geometry for the zirconium atoms with the amide N atom and the two Cl atoms being the three legs and the Cp* ring being the seat. Variable-temperature ¹H NMR experiments for all complexes 1–4 were performed to investigate the possible intramolecular interaction between the N atom in the NMe₂ group and the central zirconium atom in solution. Upon activation with AlⁱBu₃ and Ph₃CB(C₆F₅)₄, complexes 1–4 all exhibit moderate to good catalytic activity for ethylene polymerization and copolymerization with 1-hexene, producing linear polyethylene or poly(ethylene-co-1-hexene) with moderate molecular weight and reasonable 1-hexene incorporation.